Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$163.89	4.570%	$171.3798	$171.38	$171.40	$171.40
Purchase #2	$60.82	10.105%	$66.9659	$66.97	$66.95	$67.00
Purchase #3	$53.32	5.372%	$56.1844	$56.18	$56.20	$56.20
Purchase #4	$104.72	3.380%	$108.2595	$108.26	$108.25	$108.30
Purchase #5	$119.48	6.756%	$127.5521	$127.55	$127.55	$127.60
Purchase #6	$127.59	3.261%	$131.7507	$131.75	$131.75	$131.80
Purchase #7	$108.53	6.790%	$115.8992	$115.90	$115.90	$115.90
7 purchase totals =	$738.35		$777.9916	$777.99	$778.00	$778.20